Computer systems typically involve a host computer connected by cable to a peripheral unit (or "function") such as a keyboard, mouse, printer, modem, joystick, scanner, video camera, game pad, virtual reality devices, data gloves, mechanical devices, or the like. A connecting system of ports and a cable, termed a "bus", is generally one of two types, either parallel or serial. A parallel bus, usually used for printers, transmits a combination of bits (generally a byte) simultaneously over several wires in a cable. A serial bus transmits the bits in series. However, even a standard serial bus has up to nine wires for auxiliary functions such as request-to-send, data-carrier-detect and other "handshake" signals. Also, different peripherals utilize different port and cable configurations so that interchangability is limited, and a host computer usually contains several different types of ports with connectors for the different peripherals. Moreover, it is difficult to assemble a series of peripherals such as with a mouse connected to a keyboard.
Recently a group of industry leaders developed standards for an advanced system called "Universal Serial Bus", or "USB", intended for all types of computer units including peripherals. Only one pair of twisted wires is required in the cable for data transmission, although another pair provides power from a host to the peripheral units. To implement signal transmission and sufficient auxiliary information, both signal wires transmit pulses in parallel with a specified protocol or relativity of signals. During idle condition (no sending of data), one or the other is at a steady voltage with the other at zero, to indicate which of two transmission speeds are in effect. An end of a packet of data or other information (handshake, etc.) is signaled by both wires being at zero voltage before returning to idle. The host arbitrates between peripherals and the host so that while one unit is transmitting the other is in a receive mode.
USB specifications are available from the USB Implementers Forum via internet http://www.usb.org. These allow for up to 127 devices, two speeds and a maximum of 5 meters per cable segment. A computer system can have one or more "starred" hubs for multiple connections of computer units. The length limitation is related to the specifications on time delay, impedance and other electronic aspects that effect allowable noise levels. However, there is a need for longer cables, for example for a host computer controlling other computer units such as video cameras, security devices or building functions, or for connecting two personal computers at a distance.
Accordingly, an object of the invention is to provide an apparatus for extending cable length between computer units that incorporate Universal Serial Bus technology. Another object is to provide such apparatus at a modest cost.